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J M Foley

Publications and source records attributed to J M Foley.

At least 37 records · Page 2Linked to original sources
PubMed1994

Testing models of respiratory control in skeletal muscle.

We examined the relationships between PCr and Pi vs oxygen consumption or twitch rate during stimulation of rat muscle in situ and of perfused cat biceps and soleus muscles. In fast-twitch muscles such as rat gastrocnemius and cat biceps, we found a linear relationship between PCr and oxygen consumption. This result favors thermodynamic regulation of oxygen consumption by cytoplasmic phosphorylation potential rather than kinetic regulation by ADP. PCr changes during stimulation of rat muscle depleted of total creatine or adenine nucleotide were also not consistent with simple kinetic regulation by ADP. In cat soleus (slow-twitch) muscle, the observation of nonexponential PCr changes during stimulation suggested more complicated regulation, possibly involving changes in mitochondrial redox potential.

Adenine Nucleotides↗
PubMed1993

Forward pattern masking and adaptation: effects of duration, interstimulus interval, contrast, and spatial and temporal frequency.

Eight experiments are described that compare pattern adaptation and forward pattern masking by examining the effects of five variables on the contrast threshold of a target presented after an adapter or masker. The target is a Gabor pattern with a center frequency of 2 c/deg and a duration of 33 msec. Thresholds are determined using an adaptive spatial forced-choice method. Principal results are as follows. (1) An adapt-refresh regime with a 2 sec refresh and a 2 sec recovery period on each trial is shown to maintain constant performance. (2) Desensitization is very rapid, reaching near maximum in < 200 msec. (3) Recovery is very rapid during the first 100-200 msec and then very slow with the rate of slow recovery decreasing as adapter/masker duration increases. (4) Threshold vs contrast functions are step-like for certain frequency pairs. (5) Sensitivity vs frequency functions derived from adapting and masking are similar in form. (6) Masker temporal frequency (0-15 Hz) has very little effect. These results are described by a theory that postulates that the target is detected by a few mechanisms that are differentially tuned to spatial frequency. The effect of both a forward masker and an adapter is to desensitize the mechanisms that respond to it. Recovery is a weighted sum of two decay processes, one fast and one slow. The theory fits the data from both paradigms well with some differences in parameters.

Adaptation, Ocular↗
PubMed1993

Magnetic resonance measurement of blood flow in peripheral vessels after acute exercise.

Velocity-encoded Cine magnetic resonance imaging (MRI) was used to measure blood flow in the anterior tibial artery (AT), posterior tibial artery (PT), and popliteal artery of adult human subjects (mean age 29 yr) before and after 90 s of ankle dorsiflexion exercise. Before exercise, mean flow, peak systolic velocity, and end-diastolic velocity in AT were 8.1 +/- 1.6 (SE, n = 6) ml/min, 26.9 +/- 2.6 cm/s, and -0.6 +/- 0.4 cm/s, respectively. After exercise, mean flow and peak systolic velocity in AT increased by 19-fold and 3-fold, respectively, and end-diastolic velocity increased to 8.7 +/- 1.1 cm/s. Flow in popliteal artery above its bifurcation was similar to the sum of flows in AT and PT, both before and after exercise. Flow in AT declined exponentially after exercise with a mean half-time of 4 min. The results demonstrate the utility of MR phase-encoded flow-velocity measurements for physiological studies of peripheral vascular dynamics after exercise.

Adult↗
PubMed1991

Decreased ATP cost of isometric contractions in ATP-depleted rat fast-twitch muscle.

ATP was depleted to inosine 5'-monophosphate (IMP) in gastrocnemius muscles of anesthetized rats during two consecutive bouts of intermittent tetanic stimulation (each 1 Hz at 100 Hz, 100-ms duration, for 3 min) separated by 5 min. During a subsequent 75-min recovery period, resynthesis of adenine nucleotide from IMP was inhibited in one group of muscles with hadacidin (N-formyl-N-hydroxyaminoacetate, total dose 300 mg/kg ip), an inhibitor of adenylosuccinate synthase. In vivo 31P-nuclear magnetic resonance spectra and analysis of muscle extracts confirmed that ATP was reduced by over 30% in hadacidin-treated muscles compared both with nonstimulated muscles and with identically stimulated and rested control muscles in saline-injected rats. After the recovery period, calculated [ADP] in ATP-depleted muscles was half that in controls, while phosphorylation potential [PP = ln([ATP]/[ADP] [Pi]), where Pi is inorganic phosphate] and twitch force were similar. During a final 8 min of 0.75-Hz twitch stimulation, [ADP] and the initial rate of phosphocreatine (PCr) hydrolysis were less in ATP-depleted compared with control muscles, while changes in PP and twitch force were similar in the two groups. During a final 3 min of tetanic stimulation, ATP, PCr, and pH decreased less in ATP-depleted compared with control muscles. The results indicate that the ATP cost of isometric contraction is decreased by acute ATP depletion.

Adenosine Triphosphate↗
PubMed1991

Forward pattern masking: effects of spatial frequency and contrast.

Contrast thresholds of Gabor targets presented after sine-wave grating maskers were measured. All the patterns were isochromatic. The duration of both masker and target was 33 ms. The interstimulus interval was 33 ms. Masker spatial frequency, masker contrast, and target frequency were varied. Two experiments were conducted. In the first there were four target frequencies: 0.5, 1, 2, and 4 c/deg, with five masker frequencies covering a range of +/- 2 octaves around each and five masker contrasts (0.05-0.8). In the second there were three target frequencies (1.5, 2, and 2.83 cycles per degree), five masker frequencies around each, and 13 contrasts (0.005-0.8). Masking functions were bandpass, with maximum masking near the target frequency. Target thresholds increased with masker contrast. Over the shorter, sparser contrast range of experiment 1, functions appear roughly linear or concave upward. When they are plotted on log-log coordinates, functions for different masker frequencies diverge as masker contrast increases. Experiment 2 makes it apparent that some of these functions contain two increasing segments with a flat segment between them. These results are well described by a theory postulating that detection of these targets is mediated by two or three mechanisms that are differentially tuned to spatial frequency. The effect of the forward masker is briefly to desensitize the mechanisms that respond to it. The theory is fitted to the results of experiment 2, and its parameters are estimated.

Contrast Sensitivity↗
PubMed1991

Ethical issues in the management of cerebrovascular disease.

Medical ethics, as a scholarly and applied discipline, is concerned with the morality of behavior in medical matters. The field of cerebrovascular disease is a worthy paradigm of medical ethical issue. Victims, whether they be patients or their families, are vulnerable, and the ethical virtues of kindness, understanding, compassion, mercy, and justice are badly needed. A variety of hypothetical ethical scenarios faced by the physician are discussed in this article in addition to four actual patient studies with commentary.

Age Factors↗
PubMed1990

Direct relationship between proton T2 and exercise intensity in skeletal muscle MR images.

Exercise selectively increases the signal intensities (SI) of active muscles in T2-weighted magnetic resonance (MR) images. If these SI increases are graded with exercise intensity, the identification of muscle recruitment patterns may be possible using MR imaging. The purpose of this study was to determine the effect of force generation during exercise on muscle T2 values. Also, we examined the effects of extracellular fluid volume (ECV) expansion on muscle T2 values. Transaxial midcalf images were collected before and after exercise on eight volunteers in a 1.5T GE magnet using a standard spin echo sequence. Exercise consisted of three consecutive bouts of ankle dorsiflexion against graded loads. Three subjects also underwent brief bouts of lower leg venous occlusion (ECV expansion) during and in addition to the exercise protocol. T2 values for the dorsiflexors significantly increased after exercise. Greater mean force produced during exercise caused greater increases in T2 after exercise (T2 = 29.6 +/- 0.9 X Force). Exercise and venous occlusion caused equivalent increases in muscle cross-sectional area. These equivalent increases in ECV were not accompanied by equivalent increases in muscle T2; venous occlusion alone caused less than a 5% increase in T2 while exercise caused a 14% to 25% increase. Consequently, a direct relationship between increases in T2 and in ECV after exercise was not established. Venous occlusion during exercise, however, did significantly augment the increase in T2 and ECV of the anterior compartment muscles. Contrast enhancement among muscles after exercise in T2-weighted MR images is dependent on generated force during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Muscle buffer capacity estimated from pH changes during rest-to-work transitions.

Gated phosphorus nuclear magnetic resonance (31P-NMR) spectra were acquired after 5 or 9 s of 5-Hz stimulation in rat and cat skeletal muscles, respectively. Net phosphocreatine (PCr) hydrolysis was associated with an intracellular alkalinization of 0.08 +/- 0.01 and 0.05 +/- 0.003 pH units in isolated perfused cat biceps and soleus, respectively, and 0.12 +/- 0.02 in the superficial predominantly fast-twitch white portion of gastrocnemius of anesthetized rats. The net change in [H+] expected from PCr hydrolysis was calculated, and apparent buffer capacity (beta) in intact muscles was calculated from beta = delta [H+]/delta pH. The beta of the same muscle types was also estimated from titration of muscle homogenates between pH 6.0 and 8.0. The contribution of Pi to total beta of the homogenates was subtracted to ascertain the non-Pi beta for each muscle. The non-Pi beta values were added to the actual amount of Pi present in the stimulated muscles to calculate a predicted beta at pH 7. The apparent beta calculated from PCr and pH changes in intact muscles and the predicted beta from homogenate titrations were in good agreement (38 +/- 9 vs. 38 slykes in cat biceps, 21 +/- 7 vs. 30 in cat soleus, and 30 +/- 6 vs. 27 in rat gastrocnemius). The results indicate that changes in pH during the first few seconds of contraction can be entirely accounted for by proton consumption via net PCr hydrolysis.

Animals↗
PubMed1989

Utility of AICAr for metabolic studies is diminished by systemic effects in situ.

It has been reported that intraperitoneal infusion of 5-amino-4-imidazolecarboxamide riboside (AICAr) inhibits the purine nucleotide cycle, resulting in rapid fatigue of isometric twitch force during stimulation of rat muscle. In this study, peak isometric twitch force was recorded from gastrocnemius muscles of pentobarbital-anesthetized rats stimulated in situ at 0.75 Hz after intraperitoneal infusion of 9ml/100 g body wt of 250 mM AICAr or isotonic saline. Excluding the two AICAr-infused rats that died during infusion or stimulation, there was no difference in twitch force between groups, although mean arterial pressure in the AICAr group declined to values 20 Torr below those of the control group during drug infusion. High-resolution 1H nuclear magnetic resonance (NMR) spectroscopy of extracts verified the presence of AICAr and AICA ribotide (AICAR) in muscles of experimental animals. In a second study in which rats were mounted head down in an NMR spectrometer, AICAr infusion resulted in decreased mean arterial pressure and impairment of phosphocreatine recovery after stimulation but no significant difference in twitch force during stimulation. These results demonstrate that AICAr infusion has systemic effects and that the previously reported decline in muscle force with AICAr infusion may not be attributable to purine nucleotide cycle inhibition.

Aminoimidazole Carboxamide↗
PubMed1989

The hexose transporter of human erythrocytes in aging and Alzheimer dementia.

The hexose transporter protein of human erythrocyte membranes was investigated in aging and in demented patients with Alzheimer disease (AD) and Parkinson disease (PD) by assessing the D-glucose-displaceable binding of the ligand cytochalasin-B. We found no alteration in the hexose transporter of erythrocyte membranes in aging or in dementia of AD and PD. These findings indicate that the marked decrease in the density of hexose transporter that we previously reported in the cerebral cortex and brain microvessels in AD do not occur in erythrocyte membranes that have the highest density of the hexose transporter protein.

Adult↗
PubMed1987

Oculogyric crisis: a syndrome of thought disorder and ocular deviation.

In 3 patients who suffered oculogyric crises, mental changes accompanied upward deviation of the eyes. In 1 patient, whom we studied in detail, the mental disturbance consisted of a disorder of attention in which pathological fixation of a thought occurred. During the period of upward eye deviation, all functional types of conjugate eye movements were present in the upper field of gaze, suggesting an imbalance of the vertical gaze-holding mechanism. The eyes could be driven down only by a combined blink and downward saccade. Both the thought disorder and the ocular deviation responded promptly to anticholinergic agents. We propose that the disorders of thought and eye movement in oculogyric crisis are linked by a pharmacological imbalance common to both.

Adult↗
PubMed1985

Spatial frequency interference on grating-induction.

Spatial frequency interference and facilitation in suprathreshold vision were studied using the grating-induction effect [McCourt, Vision Res. 22, 119-134 (1982)] as a sensitive probe. The effects on grating-induction magnitude produced by variations in "interfering" and "inducing" grating spatial frequency, contrast and phase were examined in four experiments. A limited range of high spatial frequency interfering gratings reduced the contrast of gratings induced by spatially coextensive lower frequency inducing gratings. Both phase-dependent and phase-independent interference was observed. Facilitation of grating-induction was produced by interfering gratings of lower frequency than the inducing grating. It is hypothesized that the grating-induction interference effect is due to inhibition of the low spatial frequency selective mechanisms responsible for induction, by channels tuned to higher frequencies. The functional significance of induction and spatial frequency inhibition is discussed, and a mathematical description of the results is presented.

Form Perception↗
PubMed1985

Binocular distance perception: egocentric distance tasks.

This study extends and tests a theory of binocular distance perception that has been shown to give a good account of performance in relative distance tasks. Here the theory is tested in two experiments in which the observer directly indicates perceived egocentric distance of targets (perceived distance from himself or herself) by means of a verbal report or manual pointing response. In the first, the distance to two targets is varied while maintaining a constant disparity between them. In the second, one target is held fixed while the distance to a second target is varied. In each case, the observer indicates the perceived distance of each target. Manual and verbal responses are found to agree with each other to within a linear transform. Both sets of data are shown to be consistent with the theory and are used to estimate the parameters of the theory. There is no other theory that predicts these results.

Adolescent↗
PubMed1985

Visual grating induction.

If a homogeneous illuminated test field is inserted within a sine-wave grating, an opposite phase grating will be perceived in the test field under a wide range of conditions. A cancellation technique was used to measure the magnitude of grating induction. The manner in which the effect depends on eye movements, inducing frequency, test-field height, inducing-field height, inducing amplitude, test-field luminance, and test-field width was determined in four experiments. Mathematical equations that describe these results are presented. It is shown that linear filters whose spatial weighting functions resemble receptive fields of the most common types of visual cell do not produce outputs with the properties of induced gratings. However, linear filters with highly elongated negative end zones and a small positive center produce opposite phase gratings in the test field, and an array of such filters of different sizes can account for several properties of induced gratings. There are other properties of the effect that are highly nonlinear. A second model, which is nonlinear and based on the properties of hypercomplex cells, is suggested that may encompass both the linear and the nonlinear properties of the effect.

Adaptation, Physiological↗